Optical scanner devices are well-known in the art and may be used to produce machine-readable image data signals that are representative of a scanned object, such as a photograph or a page of printed text. In a typical scanner application, the image data signals produced by an optical scanner may be used by a personal computer to reproduce an image of the scanned object on a suitable display device, such as a CRT or a printer.
A hand-held or portable optical scanner is an optical scanner which is designed to be moved by hand across the object or document being scanned. The hand-held scanner may be connected directly to a separate computer by a data cable. If so, the data signals produced by the hand-held scanner may be transferred to the separate computer “on the fly,” i.e., as the image data are collected. Alternatively, the hand-scanner may include an on-board data storage system for storing the image data. The image data may then be downloaded to a separate computer after the scanning operation is complete via any convenient means, such as a cable or an optical infrared data link.
Hand-held or portable optical scanners are well-known in the art and various components thereof are disclosed in U.S. Pat. No. 5,552,597 of McConica for “Hand-Held Scanner having Adjustable Light Path”, U.S. Pat. No. 5,586,212 of McConica, et al., for “Optical Wave Guide for Hand-Held Scanner,” U.S. Pat. No. 5,381,020 of Kochis, et al., for “Hand-Held Optical Scanner with Onboard Battery Recharging Assembly,” and U.S. Pat. No. 5,306,908 of McConica, et al., for “Manually Operated Hand-Held Optical Scanner with Tactile Speed Control Assembly,” all of which are hereby incorporated by reference for all that they disclose.
A typical hand-held optical scanner may include illumination and optical systems to accomplish scanning of the object. The illumination system illuminates a portion of the object (commonly referred to as a “scan region”), whereas the optical system collects light reflected by the illuminated scan region and focuses a small area of the illuminated scan region (commonly referred to as a “scan line”) onto the surface of a photosensitive detector positioned within the scanner. Image data representative of the entire object then may be obtained by sweeping the scan line across the entire object, usually by moving the hand-held scanner with respect to the object. By way of example, the illumination system may include a plurality of light emitting diodes (LEDs), although other types of light sources, such as fluorescent or incandescent lamps, may also be used. The optical system may include a “contact image sensor” or CIS to focus the image of the illuminated scan line onto the surface of the detector. Alternatively, a lens and/or mirror assembly may be used to collect and focus light from the illuminated scan region onto the detector.
The photosensitive detector used to detect the image light focused thereon by the optical system typically comprises a charge-coupled device (CCD), although other devices may be used. A typical CCD may comprise an array of individual cells or “pixels,” each of which collects or builds-up an electrical charge in response to exposure to light. Since the quantity of the accumulated electrical charge in any given cell or pixel is related to the intensity and duration of the light exposure, a CCD may be used to detect light and dark spots of an image focused thereon.
The term “image light” as used herein refers to the light that is focused onto the surface of the detector array by the optical system. Depending on the type of scanner and the type of document, the image light may be reflected from the object being scanned or it may be transmitted through the object. The image light may be converted into digital signals in essentially three steps. First, each pixel in the CCD detector converts the light it receives into an electric charge. Second, the charges from the pixels are converted into analog voltages by an analog amplifier. Finally, the analog voltages are digitized by an analog-to-digital (A/D) converter. The digital signals then may be processed and/or stored as desired.
The hand-held scanner device may be provided with a position sensing or “navigation” system in order to determine the position of the hand-held scanner with respect to the object being scanned. Accordingly, such a position sensing system allows the scanner to correlate its position with respect to the object being scanned. The position correlation allows a complete image of the scanned object to be produced even though the scanner may not scan the entire object during a single pass or “swipe.” For example, if two or more swipes of the object are required to scan the entire object, then the position correlation provided by the navigation system will allow the various portions of the scanned image data to be “stitched” together to form a single unitary image representative of the entire scanned object.
One type of navigation system utilizes a pair of optical sensors to detect certain inherent structural features (e.g., surface roughness, paper fiber orientation, etc.) contained on the object being scanned (e.g., a sheet of paper with text or images thereon). Examples of the foregoing type of navigation system are disclosed in U.S. Pat. No. 5,089,712 of Holland for “Sheet Advancement Control System Detecting Fiber Pattern of Sheet,” and U.S. Pat. No. 5,578,813 of Allen, et al., for “Freehand Image Scanning Device which Compensates for Non-Linear Movement,” both of which are specifically incorporated herein by reference for all that they disclose.
While such navigation systems are known and are being used, they are not without their problems. For example, one problem associated with optical navigation systems of the type described above stems from the difficulty in uniformly illuminating the inherent structural features on the object so that the same may be detected by the navigation sensors. The light sources typically used to illuminate the navigation areas (e.g., infra-red light emitting diodes (LEDs)) typically do not provide a uniform illumination pattern. Consequently, the illuminated navigation area may comprise one or more brightly illuminated regions and one or more less-brightly illuminated regions. If the difference between the brightly illuminated regions and the less brightly illuminated regions is substantial, there is a significant chance that the navigation system will interpret the non-uniformity of illumination as fixed pattern noise, which may result in the navigation system producing a false navigation signal. Such false navigation signals may well result in erroneous position values which may make it impossible for the image data processing system to successfully stitch together the various image portions captured during the various scanning swipes.
One solution to the non-uniform illumination problem described above is to provide the light source with one or more lenses or reflectors to better distribute and focus the light onto the navigation area. Unfortunately, such lens or reflector systems may be difficult to fabricate and align and, in any event, tend to add considerably to the overall cost of the scanner. Partly in an effort to avoid the foregoing problems, most optical navigation systems utilize LEDs having integral lenses of the type that are well-known and readily commercially available. While the integral lens design avoids the problems associated with providing separate lenses or reflectors, the quality of most such integral lens arrangements is generally quite poor, and it is not uncommon for the illumination patterns produced by such integral lens LEDs to contain substantial non-uniformities. Indeed, the quality of the illumination provided by such integral lens LEDs is generally barely sufficient to allow for the consistent and reliable operation of the scanner navigation system.